Threatened semi-arid temperate scrub habitats
Nature
In most regions a long history of overgrazing, fire and wood cutting has meant that various scrub formations have replaced woodlands long ago. In some cases before 9000 BP.
The degradation of Mediterranean type environments in Chile, California, (Chaporral scrub) South Africa (Fynbos) and Australia (mallee scrub) has been going on for, at most a few centuries, but the effects are marked. In some mediterrranean areas the land may have been degraded in pre-historic/historic times and attained a post disturbance 'steady state', but is now changing to yet another, probably lower-grade steady state due to new pressures such as increased tourism, agricultural, industrial and housing development, pollution and invasive species.
While preventing fires in these regions to protect property etc the result is often a greater biomass available for future fires that will be greater in intensity and duration and cause greater damage both to the flora and to property that people want to protect.
While mediterranean type regions show clearly the impact of human activity, the problem is that available data are generally insufficient to estimate degree or rate of change in vegetation, though historical records and paleoecology can help to fill in the gaps in knowledge.
Background
Mediterranean climate. This term refers to climate belts found in both the Northern and Southern hemispheres on the western coastline of continents, approximately between 30 and 40 degrees latitude. Mediterranean climate belts receive an average of 10 to 20 inches of rainfall a year and experience only occasional frosts. These areas typically have winter rains and dry warm summers, with a fairly constant temperature. In Mediterranean climates around the world, plant species have adapted to a point that they would not exist without the presence of fire. Wildland fires spawn a period of rebirth and vigour in post-fire environments by removing dead materials and by releasing nutrients back to the environment that are locked up in mature plants and organic litter.
Incidence
The Doñana National Park in the south-west of Spain is internationally recognized for its importance to large numbers of waterfowl species as well as to many fish, reptiles and mammals including the Iberian lynx (Lynx pardinus). Doñana also contains a good example of the Mediterranean scrub habitat type of which little remains in Europe.
Scientists suggest that projected climate change in the south-west of Spain, equals a doubling of carbon dioxide concentration, leading to a decreased water availability of about 400 mm as a result of increased evapotranspiration. The longer dry season, lower soil moisture and higher evaporation would be characteristic of a climate akin to present day conditions in Libya and cause the mesic vegetation to be replaced by arid vegetation with a consequent reduction in plant diversity.
Southern California's coastline, once covered by Coastal Sage Scrub is now mostly houses, parking lots, highways, and strip malls. Only scattered pockets of Coastal Sage Scrub ecosystem in it's maritime form remain, under pressure from invasion by exotic vegetation.
An association of woody shrubs ranging in height from one to five feet, it is typified by California sagebrush, white and black sage, California buchwheat, and lemonadeberry. Plants in this community are adapted to arid coastal climates from sea level to 3,000 feet. Coastal sage scrub plants can store moisture and reduce moisture loss during the prolonged hot, dry months from May through the end of September. The plants either conserve water by specialized leaf structures or dormancy.
Type
(G) Very specific problems